The invention concerns a dewatering belt, in particular as a drying screen for paper machines, which is composed of a plurality of plate-shaped planar elements that, in order to adjust the permeability, have passthrough openings and/or leave gaps between them, the planar elements being coupled to one another, by way of flexible connecting cords which pass through the planar elements, in such a way that the longitudinal forces acting on the dewatering belt during operation act on them.
A dewatering belt of this kind is evident from DE 37 35 709 A1. This dewatering belt comprises a plurality of planar elements that are configured as elongated planar strips extending in the transverse direction, which are arranged one behind the other in the longitudinal direction of the dewatering belt and are coupled to one another by transversely extending inserted wires. For this purpose, the planar elements engage alternately into one another so as to create lined-up passages into which the inserted wires can be slid.
A dewatering belt of this kind has considerable advantages. The plate-shaped planar elements can be easily and quickly manufactured by injection molding or by extrusion methods. By combining them, it is possible to fabricate dewatering belts in almost any desired length and width. Permeability in the thickness direction can be precisely and reproducibly adapted to particular requirements with the aid of defined passthrough openings in the planar elements themselves and/or by providing gaps between the planar elements. Despite these passthrough openings and/or gaps, the paper web is supported over a large area, so that practically no marks are created on the paper web. There is also a great deal of freedom in terms of the thickness of the planar elements, i.e. they can be adapted to the particular machine requirements. A corresponding freedom exists in terms of selecting the material for the planar elements. Plastics, such as thermoplastics, thermosetting plastics, and cast resins, are suitable therefor. The planar elements can, however, also be manufactured from elastomers or even metals. It is also conceivable in this context not to manufacture all the planar elements of a dewatering belt from the same material, so that different materials can be provided in alternation.
As this type of dewatering belt has been developed, it has been found that a tensile strength sufficient for all applications could not be achieved, especially if the planar elements are manufactured from plastic. Even reinforcements of the injection-molded planar elements with glass fibers or the like provided little remedy.
It is thus the object of the invention to configure a dewatering belt of the kind cited initially in such a way that it is suitable for absorbing large tensile forces in the longitudinal direction of the dewatering belt.
According to the present invention, this object is achieved in that the connecting cords extend in the longitudinal direction of the paper machine cloth and are anchored at their ends in end pieces which can be coupled to one another. The fundamental idea of the invention is consequently to absorb the longitudinal forces occurring on the dewatering belt during operation by way of connecting cords extending in the longitudinal direction. It has been found that substantially greater longitudinal forces can be absorbed in this manner than in the dewatering belt according to the existing art, adaptation to the particular requirements being made possible by appropriate selection of the nature, cross section, and material of the connecting cords.
The connecting cords can be configured, for example, as monofilaments, monofilament twisted yarns, untwisted bundles of monofilaments, flat or oval ribbons, or the like; these kinds of connecting cords can also be braided, woven, or knitted. They can also be coated. Suitable materials are, in particular, PET, PPS, PEK, PEEK, polysulfone, PEN, thermoplastic aromatic PA, and even steel. The connecting cords should always be at least as thermally and chemically resistant as the planar elements themselves.
Anchoring of the connecting cords in the end pieces can be accomplished in various ways, for example by welding, adhesive bonding, pressing, or even looping. The end pieces can be configured as individual pieces into which only one connecting cord, or a few of them, is or are anchored. They can also, however, be configured as end strips into which a plurality of connecting cords are anchored; the end strips can also extend over the entire width of the dewatering belt. The dewatering band can easily be closed by way of the end pieces. In this case each two end pieces form a seam.
It is possible in principle to assemble a dewatering belt from a plurality of portions, each portion having at its ends end pieces that are coupled to end pieces of the subsequent portion. In general, however, the connecting cords will be allowed to extend over the entire length of the dewatering belt, so that only one seam is created.
In a further embodiment of the invention, provision is made for the planar elements to have at least two connecting cords passing through them, so that they can be properly guided in the belt plane and cannot tilt. The planar elements should preferably form transverse rows offset from one another, the connecting cords extending in such a way that they pass through mutually offset planar elements of adjacent transverse rows. This type of crosslinking imparts stability to the dewatering belt, especially in the transverse direction.
The planar elements can be of largely unrestricted configuration in terms of their geometrical contouring. In principle, they should possess geometric shapes that can complement one another in jigsaw-puzzle fashion; the planar elements can, but need not, be identical to one another. Shapes suitable for this purpose are, in particular, rectangles, but also polygons (e.g. regular hexagons or cross-shaped planar elements), which can have rounded corners.
Deviating from the geometries just described, the planar elements can also be configured as planar bars, several of which are in each case arranged next to one another in the transverse direction of the dewatering belt to form a transverse row, the planar bars of two adjacent transverse rows being arranged so that the gaps of the one transverse row of planar bars are bridged by planar bars of the other transverse row.
The material for the planar elements, like that of the connecting cords, should be adapted to particular requirements. For an application as a drying screen, heat-resistant materials such as PET, PPS, PEK, PEEK, polysulfone, PEN, thermoplastic aromatic PA, and metals such as steel or light alloys are especially suitable. If plastics are used, the planar elements can be manufactured using the injection-molding method.
The planar elements moreover can also have conformations such as those already described in DE 37 35 709 A1, i.e. they can also extend over the entire width of the dewatering belt and/or can be configured as hollow elements in order to save material and therefore weight. In this context, the hollow element configuration need not be closed, and for example can be such that the cavities communicate with one another in the transverse and/or longitudinal belt direction. Desired materials can be embedded in these cavities. The planar elements can also comprise a rigid inner support part and a plastic outer sheath surrounding it, i.e. can be of layered configuration. Different materials can also be provided for the outer and inner sides of the dewatering belt. In addition, laminated or vacuum-deposited films can also be provided, for example in order to reflect thermal radiation. Flock coatings or a coating with foam material or nonwoven fiber can also be performed.
In principle, there exists the possibility of lining up the planar elements loosely on the connecting cords, such that the connecting cords pass through corresponding passthrough holes in the planar elements. They can, however, also be joined to the connecting cords, for example adhesively bonded or hot- or cold-pressed.
According to a further feature of the invention, provision is made for the planar elements to have bending hinges in the transverse direction of the dewatering belt so that they can better adapt to deflection rollers, especially if they are relatively large in area. One planar element can also have several such bending hinges. The bending hinges can be constituted by correspondingly thinning the material cross section.
Provision is also made according to the invention for the end pieces to have loop-like passages through which, in the aligned position, a coupling wire can be inserted.
The invention furthermore proposes that the end pieces have flow-enabling passthrough openings in order to adapt the permeability of the dewatering belt, in particular for steam, in the region of the end pieces to that in the other regions, where the permeability is controlled on the basis of passthrough openings in the planar elements and/or by way of gaps between them.
Lastly, the invention provides for end pieces and/or planar elements to be assembled from two complementary halves which enclose the connecting cords between them. For this purpose, the halves should have half-channels on the mutually facing sides to receive the connecting cords. The halves are placed on either side of the connecting cords and then joined to one another. The joint can be accomplished using adhesive or heat-sealing. It is also possible, however, to provide coupling elements which engage into one another and snap-lock.